With continuing improvements in cost and performance, solid-state lasers have potential benefits as illumination components for display systems. Their inherent spectral purity, high brightness, and long operating life have sparked particular interest among designers of high-end color projection systems for digital cinema, simulation, and other high-performance imaging apparatus. However, proposed solutions for using laser light sources for digital projection fall short of what is needed for providing robust display apparatus that take advantage of this potential.
Stereoscopic projection has been one area of particular interest for cinema projection overall. Conventional configurations for stereo projection include configurations that use two projectors, one for the left eye and the other for the right eye. This basic model has been applied with earlier film-based systems as well as with digital projection equipment, from vendors such as Barco Corporation. Although such two-projector designs have successfully shown the feasibility and enhanced imaging capabilities afforded by stereoscopic imaging systems, these systems are expensive, require precision alignment to each other, and impose some additional requirements on theater design and layout.
Various types of solutions for stereoscopic projection have been presented for digital projector apparatus, including configurations that use only a single projector. These have typically included systems utilizing either of two types of spatial light modulators (SLMs). The first type of spatial light modulator used in proposed stereoscopic designs is the digital light processor (DLP), a digital micromirror device (DMD), developed by Texas Instruments, Inc., Dallas, Tex. The second type of SLM widely used for digital projection is based on liquid crystal technology, available both as a transmissive light modulator, the liquid crystal device (LCD), and as a reflective liquid crystal on silicon (LCOS) modulator.
With any type of stereoscopic projection system, some type of separation mechanism is needed in order to distinguish the left and right images that are combined on a common display screen, but are intended for the appropriate left and right eyes of the viewers. Left- and right-eye images can be separated in time, can be of different polarizations relatively orthogonal to each other, or can be of different wavelengths. Conventional two-projector systems can use any of these separation schemes as just described. Single-projector digital systems can also use any of these methods. However, because they must direct light from the same projection lens, single-projector systems inherently tend to be less efficient.
Time-sequencing systems use a “page flipping” technique. Page-flipping alternately displays left- and right-eye images to provide stereo images to one or more viewers wearing shutter glasses that are synchronized to the display refresh rates. One example of this type of display system adapted for presenting stereoscopic images to multiple viewers is given in U.S. Pat. No. 6,535,241 (McDowall et al.).
Stereoscopic systems using polarization differences provide the left- and right-eye images using light at respectively orthogonal polarizations. Viewers are provided with polarized glasses to separate these left- and right-eye images. One example of this type of display system using linearly polarized light is given in U.S. Pat. No. 7,204,592 (O'Donnell et al.). A stereoscopic display apparatus using left- and right-circular polarization is described in U.S. Pat. No. 7,180,554 (Divelbiss et al.).
Stereoscopic systems can separate left- and right-eye images by wavelength and provide viewers with filter glasses that are suitably designed to distinguish the appropriate image for each eye. One example of this type of spectral separation display system is given in U.S. Pat. No. 7,001,021 (Jorke).
While each of these approaches provides workable stereoscopic display solutions to at least some degree, there are some significant problems that remain. Shutter glasses can be relatively expensive, require on-board battery power, and require synchronization with the projection system. Light utilization and efficiency is disappointing with all of these solutions. Stereoscopic systems using polarization use less than half of the available light available at any one time. Solutions using spectral separation require twice as many effective light sources as other systems and provide reduced color gamut as a result. Embodiments of each of these types of systems require high refresh rates in order to avoid flicker and can exercise the spatial light modulators at the upper limits of their practical refresh rates. Although they are advantaged over other types of light sources with regard to relative spectral purity and potentially high brightness levels, solid-state light sources require different approaches in order to use these advantages effectively.
Another type of light modulator solution for digital projection uses a linear light modulator that uses a one-dimensional array of n micro-devices and forms a two dimensional image by forming m successive single-line images, each single-line image extending in a first direction, and then scanning these m successive line images in a direction orthogonal to the first direction in order to project an image of m×n pixels.
Among linear light modulators are grating light valve (GLV) designs, offered by Silicon Light Machines, as described in U.S. Pat. No. 6,215,579 (Bloom et al.), and others. Still other solutions have been proposed using grating electro-mechanical systems (GEMS) devices, such as those disclosed in commonly-assigned U.S. Pat. No. 6,802,613 (Agostinelli et al.).
Both GLV and GEMS devices are well-suited to projection using laser devices. However, for a number of reasons, these devices have not as yet been advanced as candidates for stereoscopic projection. With these devices, shutter-glass or page-flipping stereo separation can be used, but there is still disappointing light utilization with this technique. Stereoscopic arrangements using polarization or spectral separation can be used, but thus far have required relatively complex optical designs, requiring high parts count and fairly difficult alignment challenges. With any of these approaches, attempts to increase light efficiency have also resulted in increased system complexity and cost.
Thus far, interest in stereoscopic image projection has been directed to area spatial light modulators such as DLP (DMD) or LCD devices. There is, then, a need for digital projection solutions that take advantage of the inherent light efficiency and high resolution of GEMS and other grating electro-mechanical light modulator devices for use in stereoscopic image projection.